As in many other areas of technology, plastics components are used increasingly also in aircraft construction. Small aircraft such as gliders, motorised gliders or light motorised aircraft are nowadays built almost exclusively of fibre reinforced plastics. This applies likewise for all load carrying structures in this context such as in particular the wings. The wing is constructed of a wing shell which provides the profile, i.e. the wing profile which generates the lift and which primarily accommodates torsional load, as Well as at least one wing spar. The spar absorbs the bending moment generated by the lift. The spars are designed as fibre reinforced composites and are usually designed in the form of box spars or I-spars.
Those parts of the spars which absorb the tensile and compressive forces are denoted as flanges and are essentially horizontally orientated. The substantially vertically orientated connection between at least two flanges one above the other are denoted as a web. At present the flanges are manufactured from so-called rovings, i.e. non-woven resin impregnated mineral fibres and filaments, whereas the webs are formed of resin impregnated fibres, interconnected to form woven or nonwoven fabrics. For reinforcing against bulging, the webs are generally constructed as sandwich components.
For the manufacture of plastics profiles specifically for use as aircraft spars, two modes of construction are at present usually employed of which the one resides in that the flanges are built up by manual layering in moulds or directly in the wing shell by the superimposition of resin impregnated rovings. Thereafter, by means of at least one additional mould, at least one web as well as a bonding flange is built up between the web and the flange. When adhesively bonding together, the wing upper and lower shell an interconnection is also brought about of the upper and lower flanges of the spar by bonding together in the web the web bonding flange.
The second method provides that the flanges are likewise built up in moulds by a manual layering procedure. Thereafter, they and the web base panels are assembled, preferably around moulds, and the interconnection of the individual components is brought about by applying thereon or winding there around diagonally positioned fabrics.